SM-11044 ((L)-threo-3-(3,4-dihydroxyphenyl)-N-[3-(4-fluorophenyl)propyl] serine pyrrolidine amide hydrobromide)-binding receptor protein (SMBP) was discovered as a new protein that is bound by SM-11044, which is an agonist for β-adrenergic receptors, and by iodocyanopindolol, which is an antagonist for β-adrenergic receptors (Sugasawa, T. et al., J. Biol. Chem., 272, 21244–21252 (1997)). SMBP is a membrane protein resided at lung, ileum, and eosinophil membrane, and is believed to act as a receptor for SM-11044. SM-11044 was known to have activities to down-regulate the depolarization-mediated contraction of intestine and to inhibit migration of eosinophils, and has been believed to exert such SM-11044's functions via SMBP (Sugasawa, T. et al., J. Biol. Chem., 272, 21244–21252 (1997)).
Although the cDNA of a human SMBP was recently cloned (International Publication No. WO 98/26065), it was not reported that SM-11044 binds to any recombinant protein translated from the cDNA. In other words, there has been no report showing that a human SMBP is expressed at an elevated level to the extent that its ligand-binding activity can be measured, and, therefore, any SMBP has not yet been established in its particular availability.